1. Field of the Invention
The present invention relates to an organic electroluminescent device and method for manufacturing the same.
2. Discussion of the Related Art
An organic electroluminescent device is one of flat panel displays and has advantages of high luminance and low driving voltage. Further, since it is a self-luminescent type, it has high contrast ratio, thin profile, wide viewing angle, stability at low temperatures, easy displaying images due to a response speed of about several microseconds, and simple fabrication and design of driving circuit due to its low driving voltage of DC 5V to 15V.
Accordingly, the organic electroluminescent device is used various IT devices such as TVs, monitors and cell phones.
FIG. 1 is a schematic cross-sectional view illustrating a pixel region having three sub-pixel regions emitting red (R), green (G) and blue (B) of an organic electroluminescent device according to the related art. In FIG. 1, an organic light emitting diode E is mainly shown.
Referring to FIG. 1, the organic electroluminescent device 1 includes a substrate 10 having an organic light emitting diode E thereon and an opposing substrate 30 for encapsulation.
On the substrate 10 are gate lines and data lines 12 crossing each other to define sub-pixel regions SP1 to SP3, a power line parallel with one of the gate line and the data line 12, array elements in the sub-pixel regions SP1 to SP3, the organic light emitting diode E connected to a part of the array elements. The opposing substrate 30 functions to prevent moisture and oxygen from permeating into the organic light emitting diode E.
Even though not shown in the drawings, the array elements include a switching thin film transistor (TFT) connected to the gate line and the data line 12, and a driving TFT connected to the organic light emitting diode E. The organic light emitting diode E includes a first electrode 15 connected to the driving TFT, an organic light emitting layer 20, and a second electrode 25.
A pixel region P is composed of the three sub-pixel regions SP1 to SP3, and the sub-pixel regions SP1 to SP3 include the respective organic light emitting layers 20 emitting red, green and blue.
The organic electroluminescent device 1 display images by light emission to the first electrode 15 or the second electrode 25. Recently, considering aperture ratio, a top emission type organic electroluminescent device is manufactured that emits light to the second electrode 25 i.e., the opposing substrate 30.
FIG. 2 is a schematic view illustrating a thermal deposition method using a metal mask according to the related art.
An organic light emitting material 71 in powder form for the organic light emitting layer (20 of FIG. 1) is put in a thermal deposition device 70 having a heating means that is at bottom and side surfaces and applies entirely heat to the device 70.
In a chamber maintaining a vacuum state, when the heating means of the device 70 is operated and apply heat to the device 70, the heat is transferred to the organic light emitting material 71.
Accordingly, the organic light emitting material 71 is sublimated. The organic light emitting material gas 72 is emitted through an outlet of the device 70.
The organic light emitting material gas 72 is selectively deposited in the sub-pixel regions SP1 to SP3 on the substrate 50 through a metal mask 60 having opening portions OA1 and OA2 over the outlet of the device 70 to form an organic light emitting layer on a substrate 50.
Regarding the metal mask 60, a metal plate are patterned at both of a top surface and a bottom surface in a mask process, for example, including deposition of photoresist, light exposure, developing and etching to form the opening portions OA1 and OA2, and a shielding portion SA located between the adjacent opening portions OA1 and OA2. The opening portion OA1 at the top surface has an area different from that of the opening portion OA2 at the bottom surface.
The patterning process to form the metal mask 60 is relevant to an etching rate of the metal material of the metal mask 60 and a thickness t of the metal mask 30. In case of etching the shadow mask 60 in one direction, size difference of each of the opening portions OA1 and OA2 occurs much, and error due to area difference between the opening portions OA1 and OA2 for each location occurs much. To prevent this, the simultaneous etching for the top surface and the bottom surface is performed.
Accordingly, the area of the opening portions OA1 and OA2, and in more detail, the width (that is a width of the opening portion at the surface facing the substrate 50) is required to be at least 32 um in order that the width is in the error range permissible in fabrication.
In case that the width A of the opening portion facing the substrate 50 is less than 32 um, the opening portion OA2 at the bottom surface of the metal mask 60 should have a greater area if the thickness t of the metal mask 60 is constant.
In this case, a portion between the adjacent opening portions OA2 i.e., a width of a rib portion is very small, and this causes reduction of hardness of the metal mask 60, and thus when the metal mask 60 sags, shape deformation of the opening portions occurs.
The reduction of the thickness t of the metal mask 60 can solve this problem. However, the thickness of the shadow mask made of metal material is usually limited to 40 um, and a metal plate less than 40 um may not be produced and thus fabricating the metal mask having such thickness may be impossible.
Even though such thickness is allowed, a bearing power between each of the opening portions OA1 and OA2 becomes less and thus sagging becomes more problematic.
Moreover, when forming large-sized organic electroluminescent device having 10 inches or more, increase of the area of the metal mask 60 is required, and in this case, the metal mask 60, particularly a center portion thereof sags much due to increase of weight, and formation error of the organic light emitting layer occurs much. Accordingly, fabricating the organic electroluminescent device having large size of at least 10 inches and having high resolution of at least 250 PPI (pixels per inch) using the metal mask 60 may become difficult.
Thus, what is beneficially needed is an organic electroluminescent and method of manufacturing the same to which a thermal deposition method using a metal mask is applicable, and which can have a large size of at least 10 inches with a high resolution.